Edexcel IGCSE Biology: Double Science 复习笔记 5.1.5 Bacteria in Food Production

Edexcel IGCSE Biology: Double Science 复习笔记 5.1.5 Bacteria in Food Production

Bacteria in Food Production


  • Microorganisms can be used by humans to produce foods and other useful substances
  • As well as fungi (e.g. yeast used to make bread), bacteria are also used in the production of certain foods
  • Bacteria are useful because they are capable of producing complex molecules (e.g. certain bacteria added to milk produce enzymes that turn the milk into yoghurt)
  • They are also useful because they reproduce rapidly, meaning the amount of chemicals they can produce can also rapidly increase




Using bacteria to make yoghurt

  • Yoghurt is made in a process that relies on the presence of a specific type of bacterium – in this case, Lactobacillus
  • First, all equipment is sterilised to kill other, unwanted bacteria and to prevent chemical contamination
  • Milk is then pasteurised (heated) at 85-95°C to kill other, unwanted bacteria
    • Contamination with other bacteria could slow production of the yoghurt by competing with the Lactobacillus for the lactose in the milk
    • It could also spoil the taste of the yoghurt


  • The milk is then cooled to 40-45°C and Lactobacillus bacteria is added 
  • The mixture is incubated at this temperature for several hours, while the Lactobacillus bacteria digest milk proteins and ferment (digest) the sugar (i.e. the lactose) in the milk
  • The Lactobacillus bacteria convert the lactose into lactic acid and this increased acidity sours and thickens the milk to form yoghurt
    • This lowering of the pH also helps to prevent the growth of other microorganisms that may be harmful, so acts as a preservative
    • This means the yoghurt can be kept for a longer time (compared to fresh milk)


  • The yoghurt is then stirred and cooled to 5°C to halt the action of the Lactobacillus bacteria
  • Flavourings, colourants and fruit may be added before packaging



Industrial fermentation

  • Fermenters are containers used to grow (‘culture’) microorganisms like bacteria and fungi in large amounts
  • These can then be used for brewing beer, making yoghurt and mycoprotein and other processes not involving food, like producing genetically modified bacteria and moulds that produce antibiotics (e.g. penicillin)
  • The advantage of using a fermenter is that conditions can be carefully controlled to produce large quantities of exactly the right type of microorganism






A diagram of an industrial fermenter used to produce large quantities of microorganisms




Controlling Conditions in an Industrial Fermenter Table